1. Field of the Invention
The present invention relates to a control apparatus for driving a fan with electric motors.
2. Description of the Related Art
A motor fan control apparatus for controlling the rotational speed of a motor fan for blasting air onto a radiator for carrying out heat exchange for engine cooling water and a condenser for carrying out heat exchange for coolant in an air conditioner has been known. The radiator and condenser are mounted at the front of a vehicle. With this sort of control apparatus, the rotational speed of the motor fan is controlled based on engine cooling water temperature, an air conditioner running state/stopped state, air conditioner coolant pressure, and vehicle speed etc.
FIG. 14 is a circuit diagram of a conventional pole-changing type motor fan control apparatus. With this conventional control apparatus, a radiator and condenser are cooled by cooling air generated by fans respectively attached to two 4-pole direct current motors. The number of drive poles of the two 4-pole direct current motors 1 and 2 is switched between two poles and four poles by two relays 3 and 4, and rotational speed is controlled in two stages, namely low speed and high speed. The 4-pole direct motors 1 and 2 are respectively provided with two armature winding terminals (hereafter simply called terminals) P1 and P2 for connecting to positive pole brushes, and two armature winding terminals (hereafter simply called terminals) N1 and N2 for connecting to negative pole brushes.
Also, in FIG. 14, the relays 3 and 4 are turned on (coil energized) or off (coil not energized) by a controller 11 to switch the number of drive poles of the motors 1 and 2. Voltage is supplied from a battery (B) 12 through fuses 13 and 14 and the relays 3 and 4 to the motors 1 and 2. Voltage is supplied from an ignition power source (IG) 15 through a fuse 16 to the coils of the relays 3 and 4. The ignition power source 15 is a power source which is effective as long as an ignition switch (not shown) is set at an ON or START position.
At the time of low speed operation, the direct current motors 1 and 2 are both driven by two poles. That is, only relay 3 is turned on by the controller 11, the battery power source 12 is only applied to the terminal P1 of the two motors 1 and 2, and current flows from the each terminal P1 of the motors 1 and 2 to the each terminal N1 of the motors 1 and 2. On the other hand, at the time of high speed operation, the direct current motors 1 and 2 are both driven with four poles. That is, the relays 3 and 4 are both turned on by the controller 11, the battery power source 12 is simultaneously applied to both terminals P1 and P2 of the two motors 1 and 2, and current respectively flows from the each terminal P1 of the motors 1 and 2 to each terminal N1 of the motors 1 and 2, and also from the each terminal P2 to the terminal N2 of the motors 1 and 2.
FIG. 15 is a circuit diagram of a conventional serial-parallel switching type motor fan control apparatus. With this conventional device, a radiator and a condenser are cooled by cooling air generated by fans respectively attached to two 4-pole direct current motors. The connection of the two 4-pole direct current motors is switched between serial and parallel by three relays 5-7, and rotational speed is controlled in two stages, namely low speed and high speed. In FIG. 15, parts that are the same as those in FIG. 6 have the same reference numerals assigned thereto, and it""s description is omitted. Also, with this serial parallel switching system, + side terminals P1 and P2 of the 4-pole direct currents motors 1 and 2 are connected, and xe2x88x92 side terminals N1 and N2 are connected.
At the time of low speed operation, the direct current motors 1 and 2 are connected in series with four poles. That is, if only the relay 5 is turned on by the controller 11, the battery power source 12 is applied to the terminals P1 and P2 of the motor 1, and current flows from terminals P1 and P2 of the motor 1 to the terminals N1 and N2 of the motor 1. Current flowing from the terminals N1 and N2 of the motor 1 then flows through the relay 6 and from the terminals P1 and P2 of the motor 2 to the terminals N1 and N2 of the motor 2. On the other hand, at the time of high speed operation, the direct current motors 1 and 2 are connected in parallel with four poles. That is, if the relays 5-7 are all turned on by the controller 11, the battery power source 12 is applied simultaneously to the terminals P1 and P2 of the motor 1 and to the terminals P1 and P2 of the motor 2, and current flows from the terminals P1 and P2 of the motor 1 to the terminals N1 and N2, and also from the terminals P1 and P2 of motor 2 to the terminals N1 and N2.
With the above-described pole changing type rotational speed control apparatus, the number of relays is small, so the circuit cost is low. However, at the time of low speed operation, motor efficiency becomes low, since the motor needs to be driven with two poles, and there is a problem that the useful life of the brushes becomes short due to high electrical load.
On the other hand, with the above described serial-parallel switching type rotational speed controller, at both low speed and high speed the motor is driven by four poles, and so the useful life of the motor becomes prolonged. However, since the rotational speed is low at the time of low speed operation, it is often used in high speed operation, and there is a problem that there is a lot of fan noise.
Also, with both types of motor fan controller, since it is not possible to control rotational in two stages for low speed operation and high speed operation, it is often used in high speed operation, and there is a problem that the electrical power consumption and the noise are considerable.
The object of the present invention is to make it possible to reduce an electrical power consumption of a fan motor and amount of noise of a motor fan, and to increase the useful life of the fan motor.
In order to attain the above-noted object, a control apparatus for two N-pole direct current motors receiving power from a single power source, for respectively driving two motor fans, comprises: a switching device that switches between a motor serial connection state where the two motors are connected in series and a motor parallel connection state where the two motors are connected in parallel, and switches a number of drive poles of the two motors, and a controller that controls said switching device so that rotational speed of the two motors is controlled in multiple stages by switching the number of drive poles of the two motors and switches the serial or parallel connection states of the two motors.
The N-pole direct current motor can be a 4-pole direct current motor or 3-pole direct current motor.